Unstable ring resonator with a compact output beam: description and experimental evaluation.

A novel type of unstable resonator is described, and its operation with a CO(2) laser is discussed. The laser mode is rectangular in cross section, and the field is inverted about a line that makes a 45 degrees angle with the edge of the beam during a round-trip pass. Beam inversion, low magnification, and reasonably low sensitivity to misalignment allow efficient power extraction from low-gain lasing media while also outcoupling a solid rectangular beam. A beam quality of 1.1 was observed. The beam quality varied from 1.1 to 1.6 during misalignment of the rear rooftop mirror by ~0.06 mrad. A further misalignment of ~0.03 mrad stopped the lasing.

Variable phase grating optical aberrator.

We have developed and analyzed a heated laminar airflow device which introduces easily varied aberrations into optical beam trains. The aberrator produced nearly sinusoidal optical path differences of modulation depth 0 to 2lambda (peak to valley) at a 355-nm wavelength and a spatial frequency of ~2 cycles/cm. The phase modulation was measured via lateral shearing interferometry and agreed with a sinusoidal near field phase model to ~10%. The far field intensity profile was in qualitative agreement with the theory of focused sinusoidal phase gratings.